When hydrocarbons, a primary component of fuel, are heated to high temperatures the hydrocarbons can decompose to form coke, a solid carbonaceous material. Coke typically consists of approximately 80% to 95% carbon by weight with the balance comprising sulfur, nitrogen, oxygen, hydrogen, and trace amount of inorganic materials (e.g., ash). Coke produced during hydrocarbon decomposition can form deposits on the walls of fuel passages, fuel nozzles and heat exchangers. As these coke deposits build up over time, the flow of fuel through the passage or nozzle can become restricted. Additionally, coke deposits can reduce the effectiveness of heat transfer within heat exchangers. If left unchecked, continued coke deposition on wall surfaces can lead to system failure.
In fluid catalytic cracking applications, coke can be produced in the cracking reactor and deposit on the cracking catalyst, thereby poisoning the cracking catalyst. Coke deposits reduce the effectiveness of the cracking catalyst. Poisoned cracking catalysts must be subjected to costly and intensive regeneration processes in order to improve their effectiveness.
U.S. Pat. No. 7,513,260 (“the '260 patent”) describes using water to remove coke deposits from the walls of heat exchangers. According to the '260 patent, water present in a fuel stream reacts with a coke deposit to produce hydrogen and carbon monoxide. This concept provides a useful method of reducing coke deposition. Water is not soluble in the fuel, however, and the method requires the use of a water/steam supply system to incorporate the water into the fuel. This water/steam supply system adds complexity, cost and weight to the overall fuel delivery system.